The criteria your customers will use to make the final buying decision (which solution to choose from which vendor) can shift over time. I hope you are keeping in touch with your Sponsor(s) and can check in with them regularly to see if they have added criteria, made some criteria more or less important than originally thought, eliminated some criteria, etc.
Even when acting in your Coach role, draw on the Architect’s toolkit to flesh out the criteria:
Do diagnostic probing (if needed)
Establish the solution criteria
Plant a seed
Turn intangibles into tangibles; vague criteria into specific