An HK94 is a 9mm, the HK93 is the .223 caliber.
I have some experience with this problem. When building a HK94 receiver, it is rolled from a "flat" and the parts are welded to it. During the finishing process usually the lands that are designed to act as an attachment point are not addressed. It is quite common to leave them as is. The more proficient builders will mill the mounting points so that the claws of the scope mount will be able to grab correctly on a flats surface. HK did this to the 94's and all of their 9 series delayed roller bolt rifles. The customary scope mount for these rifles from HK is the claw mount. It is my understanding that these mounts were individually modified to better work with a specific firearm. I purchased one for a PTR-91 and it did not require any modification.
I have a clone HK94 pistol that I wanted to mount a sight on it, and chose to buy an aftermarket low rail mount. My gun did not have the attachment mounts properly milled and it did not fit correctly. The mount had to have the claws slightly modified with a dremel to remove excess length for a proper fit. I do not have the skill to properly mill the lands on the receiver, due to the sheetmetal construction, the tolerances must be closely monitored.
If it was my HK93, I would try one of the HK claw mounts, either the HK or one of the cheaper clone mounts.