Though I don't know if Luna invested in some sort of internal bra or if her breast pocket is somehow incredibly high, but she is a good example for pointing out that when your boobs are high & round and at armpit level to start, even at 4k you are experiencing how the width of your boobs influences arm movement ability. And the bigger and wider they get, the more pronounced the effect. I found this screenshot to exhibit what I am talking about; Luna's upper arm is pressed against her boob while Foxy, despite being very much bigger, does not experience the same thing.
I think everyone would agree that if your boobs interfere with normal arm movements, that is an inconvenience, however, if you really love having huge boobs, I contend it is a pleasant one, one that makes you take into account the size of the boobs you adore, almost constantly. When you reach forward, your upper arms are held at a certain level, supported by your boobs; if what you are reach for is at a lower level, you have to bend at the waist to lower the level of your hands.
I like to picture Foxy with boobs higher, like Luna, where if she wanted to reach a doorknob, she wouldn't do so reaching over her boobs, but turn slightly sideways so she could actually see what she is reaching for and so her boobs do not prevent her from reaching it. This would be similar to what we see on the previous page after she hikes her boobs onto the table, if that isn't good enough, now imagine them even bigger, maybe each boob 3-4" taller and wider, could she even reach a napkin lying in front of her boobs on the table with 20k boobs? I hope it isn't evil of me to hope that Foxy would like to experience this, that she would love having boobs so huge that they created endless huge boobie problems, and that she loved experiencing them.