I'll put the capital ships mater on hold for a little while. This time I'll talk about the At-AT vs Snowspeeder as Vaderios pointed out to me that Ady wishes to fix this issue. I hope it will help visualize the matter.

Let's start with the snowspeeder size:
The 1/1 scale set:

The destruction model insert with live actor:

The scaled model used for SFX:

Those three images are pretty consistent with the rest of the snowspeeder shots and are portraying a snowspeeder of approx 5.3m length.

Now the AT-AT.
Below the most obvious scale establishing shot of the At At is portraying a length of about 30 m length (height varying between 24 - 26 m, depending of the stance):

it's consistent with all these shots (red lines are for the 30m ATAT):
(considering the perspective)

(assuming Luke is standing next the furthest foot)

It's working a little less well below but it's not far (red lines are still for the 30m ATAT):

-in this one the windscreen is a little too large:

-in this one the snowspeeder seems a little small to me (actually it's hard to tell given the speed & the moving nature of the shot):

The crushing scene however shows an AT-AT foot that would make a 18.5 m AT-AT, not very convincing and inconsistent with all the above said. I'd say it has to be fixed (as said on Ady's tread). (the red lines are the 30m ATAT & the green ones the 18.5m ATAT):

I've made a mockup with a foot scaled up to 140% (to make a 30m length AT-AT).
The original shot:

My mockup:

And here's my conclusion chart:

Give me your thoughts.