Store performance will affect the budget for merit increases, but it does not, I repeat, DOES NOT change the percentage associated with the various review scores. Stores with a lower budget will not be able to have as many EXs and Os as a similar store with a higher budget. A golden contribution AAA Super will have a larger merit budget than a golden contribution ULV, but the super's budget for raises will also have to spread across more tms. So in that instance, the tms at the AAA Super may not see as great of raises as the tms at the ULV. A mid range Pfresh might have less staff to give merit raises to than another mid range PFresh that has the same merit budget. This can and will have an effect on the merit score you see and therefore the associated raise you receive, but the percentage of your merit raise is based solely on your review score.
The only time you will see a raise percentage that is less than what it would normally be is if you are capped at your paygrade. If you are capped you only receive a merit raise if you are scored an EX or an O, but the percentage is less than it would be if you weren't capped (1% and 2% respectively, I think). Even if you have not been there a full year or you weren't there long enough for a review during the previous year, you will receive the normal raise percentage (assuming you aren't capped), but it will be prorated for the amount of time you have worked since your last review. This prorated amount can be for anywhere from 3 months to 15 months depending on your hire date. I started just a few months before review time and didn't hit my 90 days until right after merit raises and reviews happened. My first raise was prorated for 14 or 15 months.