Rachael was facing 5A, and therefore the plastic 'window'. She was pretty much opposite to Gerry, who had his back to 5A and the window. If he looked at Fiona and Kate he would see what was behind them which was the Tapas reception. Unless his peripheral vision is superhuman, he couldn't see 5A from his seat without turning round.
you are not correct, Gunit. You have to zoom into Google Earth and be aware of exactly how far round the table Gerry sat. 40* is nearly 45* which is an angle that most of us are familiar with.
Kates drawing, whilst being neat, has the various people incorrectly spaced ... and that is misleading.

5A was not immediately across (behind) from the table. Some of the more westerly flats in block 5 were immediately behind Fiona ... but 5A was not. 5A was in more of an easterly direction, along a bit.
My screen is extra wide so I cant measure angles precisely (as I can distances). However, it appears that Gerry is rather more facing 5A than having his back towards it. It looks like the angle that Gerry is at to apartment 5A is about 50* . So he is shoulder on, with Fiona more or less in front of his line of vision to 5A.
However these angles are as in a perfect world
Kate and Gerry were there first and obviously made room for Fiona. Gerry is a big and expansive man and I cant see him having less than his share.
Also he was basically an excellent and caring father to his young family, as can be seen from videos on the internet ... and can be heard from various people who knew them.***
WE dont know, but I think it quite likely that he would chose his exact position bearing in mind his ability and view to visually check 5A.
In other words with his size and expansiveness, I find it doubtful that he would have less than his 40* portiion but would more likely have a little more to ensure his ability to see 5A.
But we cant be certain, can we ?
*** No, I am not giving cites because it is common knowledge