How much subfloor 'dip' is acceptable?

Sorry if this has been covered in other threads -- I can't find it.

In my bathroom, currently under DIY remodel, I've got new 3/4" plywood on top of 16" o.c. 2x10 joists, with the longest unsupported joist span only 5 feet. (Not sure if any of that is relevant to my question but I thought I'd throw it in there.)

Running a long level over the finished subfloor I see there are a couple of spots where it dips 1/8". I'm wondering if that's enough to worry about. I'm planning to put in 12x12 ceramic tile.

My plumber has offered to do the tile floor and said he'd do a 'mud job', which I gather would obviate any need to worry about the dips.

But I'm also thinking of trying it myself, with 1/2" Durock as underlayment. (I know, everyone likes Kerdi, but I need the height and I've used it before, though only on walls.) If I go that route, are 1/8" dips enough of a problem that I'd have to get out the self-leveling compound and fix it before putting in the underlayment, or would the mortar in which I (gather I'm supposed to) embed the underlayment deal with that amount of 'dip' adequately?

I'm probably being exessively anal but I want to make sure. After all this work I'll kill myself if the tile cracks because of voids under the underlayment.

Thanks for help.