Sketch won't properly export my assets in the correct scale

I have a group of assets (buttons) all different sizes so i'm counting on the batch re-sizing of Sketch, but since Sketch 3 I'm not so sure I understand how the resizing is working.

For example if I have a buttons that is 25x25 then when I export @1x I expect it to export at the exact size of 25x25; and that's normally what will happen.

But when I try to scale up to 2x or 3x I sometimes get 3 times the size when I put 2x and at other times I get 4x sizes for putting 3x.

So some might say "oh that's an easy fix" just use for your 2x to mimic 3x sizes and 4x to mimic 3x sizes but that doesn't work either.

I can't sit here and export each asset one by one to use the custom width feature that Sketch supports either in where you can enter for example 830w and it will make that the width of the image and automatically determine it's height based on width.

This is so frustrating and has turned a feature that was once a pleasure to use into more work than it's worth. This has been my major gripe about Sketch 3.0 and i've been a paying customer since day one.

Anyone else encounter this issue?

Thanks.