I think it could also be put down to size. The Riptide is much larger than XV8 scale suits, bigger even than broadsides and XV9s.
There could understandably be a trade off in terms of strength and size. Smaller shield fields are more concentrated and focused, and are therefore stronger than large shields which have to spread the energy further from the generator itself. This is also seen in comparing the shield drone with the guardian drone. Shield drone has a more powerful field, but it focuses on the drone itself, guardian drone spreads the shield over an entire squad, but it is weaker.
It wouldn't even matter if you had a more powerful generator, as energy will naturally dissipate as it gets further from the source, so making it more powerful would serve to strengthen it closer to the generator but it would still become weaker the further it got from the source.
Technically, if you could increase the initial power source by sufficient magnitude, you could make a larger shield more powerful, such as with base shields, or starships. The Riptide used to be able to overcharge the nova reactor to boost it's shield to a 3++ meaning that it would be both larger, and more powerful.