There is a difference, because you're not using an initial term in yours, there is no trial amount, so there's nothing to apply the "trial amount only" coupon to.
There's the regular payment term of the subscription, and then there's the trial term, which can be free or paid. This term is separate from the regular term.
If you want to apply a coupon to a subscription, if applied to the regular term, then all payments will be at the discounted price. To discount only the first payment, a trick is to add an paid trial term (aka initial term), even if it's practically the same as the regular one in terms of time and money. But it's separate, and that allows you to apply a discount there without affecting also the following payments.
Does it make more sense now?