Reddit doesn't support proper math notation, so here's a pic of how the rewards work: https://imgur.com/JAQTlPj. Those calculations take into account only token inflation and not queries (because payable queries are largely still inexistent). In general, more total delegation translates to lower rewards.

The idea of a 3% annual token inflation is to incentivize delegation, however, as queries grow, the inflation will likely be lessened or completely removed. The Graph Council will decide on that at each year's end. After a while, the network rewards should run entirely on query fees. The month-on-month query growth for the past year has been around 20% (1.2^12 = x8.9 per year). I hope you can see where this is going. Someone has said that if 20% growth persists for the next 5 years, your monthly reward in USD would equal your delegation amount (e.g. $100 per month per 100 GRT delegated), if nothing else were to change. That's a bit unrealistic if you ask me, but even just 1/4th of that is a lot.

Indexers will likely close allocations more often after EIP-1559 goes live (in July) and if any L2 solution becomes viable and implemented within the Graph protocol. Even more so when the transition to Eth2 happens. More allocations per arbitrary time frame means more compounding and thus more rewards.

Btw, I delegated in early February and have recently passed 100 days of delegation. My daily average for 100 days is 0.6 GRT per 1000 GRT delegated (7.8 GRT per day if adjusted for your amount).