Safe Harbor plan with discretionary match using flexible discretionary formula

Plan is a safe harbor plan meeting safe harbor a 100% match on the first 4% of deferrals.

Plan has a flexible discretionary match that would generally meet ACP safe harbor requirements except that plan sponsor only wants to match pre-tax deferrals. Two NHCEs make Roth contributions, no HCEs make Roth.  I think that is a problem because the ratio of matching would be higher for HCEs than NHCEs. Plan would pass ACP testing, but I still don't think they can exclude Roth deferrals from the discretionary because they specifically elected that both the "ADP and ACP test safe harbor" provisions will be used for any Plan Year in which any type of matching contribution is made.

Since they've elected that ACP safe harbor provisions will be used, I think that they have to use the safe harbor provisions and can't revert to ACP testing.

Am I missing something?  This is a takeover plan for us and in prior years the service provider did allow the discretionary match to be made only on pre-tax deferrals.

Thank you for any guidance.