Site : https://civitai.com/models/695458/ass-size-slider-ponyxl?modelVersionId=778270

Trained on Pony Diffusion V6 XL.

LORA weight: 0 to 5+

This is a slider, Lora, so you can choose whatever weight you want, so experiment and find what suits you best. A positive weight adds Ass size. You can use even higher weights such as 8 and above it all depends on characters and checkpoints.

You can also add Huge butt to your prompt to make it have an even stronger effect.