USPS FDC Digital Cancel Service. Do Monarch Envelopes Work?

This will be my first time sending stamps in for First Day Cancel Service and am seeking tips from the SCF. I read the postal bulletin which includes the:

Deadline for each issue and mailing address
Amount to enclose for the service (cost per envelope)
Minimum and maximum envelopes
Return postage SASE if you don't want them returning through the mail individually
Two test envelopes

Also says a 6 3/4 envelope, which appears a standard size.

My question is would a Monarch envelope which measures nearly 7 1/2, be rejected for digital service? Dont want to make them and then have either returned unserviced, or with the basic black FD cancel.

Any other tips?

With respect to DCP's, instructions here say #6 or #10:

https://about.usps.com/postal-bulle...info_007.htm

For the recent Coast Guard stamp I submitted post cards printed online at Zazzle, and they accepted them for DCP's. These were taller, and not quite as long, as #6. I've seen Maximum cards with DCP's, and other sized post cards. Since Monarch size is between #6 and #10, I cannot imagine them not being accepted.