Storage fund is showing me a 6.1% going-in cap on assets they haven't bought yet

Working through a $75m storage fund, first close done, second close is the one I'd be in. Blind pool apart from two seed assets.

The model shows a weighted average going-in cap of 6.1% on the target pool and an exit at 5.9%. Development sleeve is underwritten to a 7.4% yield on cost with a 30 month lease-up to 90% physical. Rent growth in the model is 3% annually starting in year two, flat in year one. Expense growth 3.5%.

What bothers me is that the 6.1% going-in is an assumption about deals that don't exist yet, and the exit at 5.9% is an assumption about a market five years out. So two of the three biggest drivers are inputs, and the third, the lease-up curve on the development sleeve, is the one thing they have some control over and it's underwritten faster than either of the seed assets actually leased.

I ran the exit at 6.4% instead of 5.9% and held everything else. Net to LP drops from a low teens IRR to high single digits, still above the 8% pref but the promote mostly evaporates. Which tells me the GP is being paid for cap rate compression more than for operations.

I'm trying to decide whether to ask them to re-run the model at a flat exit cap and see what the sponsor says, or whether that's a conversation that just gets me a polite deck and no change. Anyone found a version of that question that actually gets a straight answer?