A method of determining a multitude of M =2 complex, frequency dependent constants W i (k)', i =1, 2, representing an optimized fixed beam pattern of a fixed beamformer filtering unit for providing a beamformed signal Y as a weighted combination of said multitude of electric input signals IN i, i = 1, 2, to the beamformer filtering unit, where IN i are electric input signals provided by a multitude of microphones ( M BTEi, i =1, 2) of a hearing aid comprising a BTE-part adapted for being located at or behind an ear of a user, the BTE-part comprising said multitude of microphones, wherein said beamformed signal Y can be expressed as Y k = W 1 k ′ ⋅ IN 1 + W 2 k ′ ⋅ IN 2, and wherein said beamformer filtering unit comprises first and second fixed beamformers (BF1, BF2), each being defined by first and second sets of complex, frequency dependent weighting parameters ((W 11 (k), W 21 (k)), (W 12 (k), W 22 (k))), so that BF1(k)=W 11 (k)IN 1 + W 21 (k)IN 2 and BF2(k)= W 12 (k)IN 1 + W 22 (k)IN 2, and so that Y(k)=BF1(k) - β(k)BF2(k), where β(k) is a frequency dependent parameter controlling the shape of the directional beam pattern of the beamformer filtering unit, the method comprising • Determining respective transfer functions H BTEi (θ, φ, r, k) and H ITE (θ, φ, r, k) from sound sources S located at spatial coordinates (θ, φ, r) around the hearing aid to the multitude of microphones (M BTEi, i = 1, 2), and to a microphone located close to or in the ear canal, (θ, φ, r) representing spatial coordinates and k being a frequency index, and • Determining said complex, frequency dependent constants W i (k)', i = 1, 2, to provide a resulting transfer function H pinna θ φ r k = ∑ i = 1 2 W i k ′ ⋅ H BTEi θ φ r k, • so that a difference between the resulting transfer function H pinna (θ, φ, r, k) and the transfer function H ITE (θ, φ, r, k) of a microphone located close to or in the ear canal fulfils a predefined criterion, CHARACTERIZED IN THAT said predefined criterion comprises ∘ determining W 1 (k)' and W 2 (k)' by minimizing an expression for a distance measure between the resulting transfer function H pinna of the beamformed signal Y(θ, φ, r, k) and the transfer function H ITE (θ, φ, r, k) of a microphone located at or in the ear canal with respect to said parameter β(k), or ∘ determining W 1 (k)' and W 2 (k)' by minimizing a difference between a directivity index or a front-back ratio for a directional response of the beamformed signal compared to the directivity index or the front-back ratio, respectively, for a directional response of said microphone located at or in the ear canal with respect to said parameter β(k). • Determining respective transfer functions H BTEi (θ, φ, r, k) and H ITE (θ, φ, r, k) from sound sources S located at spatial coordinates (θ, φ, r) around the hearing aid to the multitude of microphones (M BTEi, i = 1, 2), and to a microphone located close to or in the ear canal, (θ, φ, r) representing spatial coordinates and k being a frequency index, and • Determining said complex, frequency dependent constants W i (k)', i = 1, 2, to provide a resulting transfer function H pinna θ φ r k = ∑ i = 1 2 W i k ′ ⋅ H BTEi θ φ r k, • so that a difference between the resulting transfer function H pinna (θ, φ, r, k) and the transfer function H ITE (θ, φ, r, k) of a microphone located close to or in the ear canal fulfils a predefined criterion, CHARACTERIZED IN THAT said predefined criterion comprises ∘ determining W 1 (k)' and W 2 (k)' by minimizing an expression for a distance measure between the resulting transfer function H pinna of the beamformed signal Y(θ, φ, r, k) and the transfer function H ITE (θ, φ, r, k) of a microphone located at or in the ear canal with respect to said parameter β(k), or ∘ determining W 1 (k)' and W 2 (k)' by minimizing a difference between a directivity index or a front-back ratio for a directional response of the beamformed signal compared to the directivity index or the front-back ratio, respectively, for a directional response of said microphone located at or in the ear canal with respect to said parameter β(k). ∘ determining W 1 (k)' and W 2 (k)' by minimizing an expression for a distance measure between the resulting transfer function H pinna of the beamformed signal Y(θ, φ, r, k) and the transfer function H ITE (θ, φ, r, k) of a microphone located at or in the ear canal with respect to said parameter β(k), or ∘ determining W 1 (k)' and W 2 (k)' by minimizing a difference between a directivity index or a front-back ratio for a directional response of the beamformed signal compared to the directivity index or the front-back ratio, respectively, for a directional response of said microphone located at or in the ear canal with respect to said parameter β(k).