I still don't see how the referral bonus work here, if it's applied to the interest rates. Anyway, that's a good way to support the project.
If each person in your referral tiers have 2 referral who loaned $100 each. Below is a summary of your daily interest:
Tier 1 - 2 person - $200 - 0.25% = $0.50 daily
Tier 2 - 4 person - $400 - 0.20% = $0.80 daily
Tier 3 - 8 person - $800 - 0.15% = $1.20 daily
Tier 4 - 16 person - $1600 - 0.05% = $0.80 daily
Tier 5 - 32 person - $3200 - 0.05% = $1.60 daily
In total you could earn $4.90 daily or $147.00 monthly.