The size is about the same. It really depends on how you draw botj of them to scale. While people like to point out that Sasuke's susano was smaller than a juubidara meteorite. Then compare it to an edo madara tengai shinsei, juubidara meteor made tengai shinsei meteor look like a small rock and made entire mountains pale in size. Madara's ps was roughly the size of his tengai shinsei if not a BIT taller
Meaning madara"s ps size is way below his juubi jin "pebbles", makong both sasuke's and Madara's ps the same size. All ps seem to be the size of a mountain. Except for Indra's, his PS looked abnormally huge when compared to Asura avatar. This may hint that a user can manipulate their perfect susano size as they see fit. On that notion to dispell other contradiction such as:
FAQ:
1) Madara's ps covered a full body susano so it must be bigger than Sasuke's right?
Answer: Majestic armor used by madara can cover almost anything it isn't just relative to the size, for example Sasuke covered full body Kurama in boruto the movie and yang Kurama before rikoudo powers, this is not relative to a power difference but the natire of the majestic cloak
2) (see above)
3) If Madara's ps isn't bigger then why is Sasuke's seen so small when opening up his susano wings after IT and Madara's stands tall
Answer: there is a significant size difference between crouching and standing. Someone that is 6'2 while they are sitting down may not appear big when you're standing above them, say someone was 6'2 but when that person sitting stands up you realize they are taller than you presumed
4) Are susano size relative to power?
Answer: there is no causation or solid fact that susano size is relative to the user's powers. These are just fabrications concocted by fans. Regardless of the power if the user, the susano size remains the same, susano would at best change in context of color, weapon, and/or posture. Each ps is roughly the size of mount everest post-explosion if not bigger. The exception to this is possibly Indra but we've never seen a full body scan of his ps, even then nobody in their right mind who understands naruto thinks Indra is stronger than Sasuke
5) can ps size be manipulated?
Answer: possibly, as mentioned each PS is roughly the size of a mountain, however in boruto the mamga Sasuke fit it inside of a relatively small cave and Indra's appeared larger than Ashura's avatar
6) Sasuke still sucks though
Answer: thanks for sharing