This sort of hard coding of size and layout is all through our code (I realise this is not something that you've added, just changed the values, but I think it deserves a comment).  I think ideally we should be sizing things proportionally.  e.g. in this case, the height of the map should be set such that say 8 rows can fit in the parent container.

Another example is say at a high level, the horizontal split of layer chooser, map panel and details panel should be something like 0.25, 0.50 and 0.25 respectively.

The reason for doing things this way is so that the UI still looks "nice" at different sizes and ratios.

Note 1: it does make sense to hard code minimum sizes, because certain components are only useful when they are at least a given size (e.g. maps).
Note 2: perhaps it is ExtJS which is preventing us from taking the above approach, but we should at least investigate and/or try.