1 stop off would be enough to ruin slide film, even with proper bracketing in +1/2 -1/2 manner.
KR5 Super 2 looks like a great camera, similar to my Carena in many regards Thumbs up!
I've used flat, featureless surfaces: wall, cloth, table, lcd, ground, with daylight, fluorescent and tungsten light where possible. Metering pattern has little to do in such cases, but I always remember to set focus to infinity, I think focusing from 0,25m/10in would result in measurable brightness drop, this is how close my 28mm lens would go. Regarding pattern, there are some cameras that are compensating for backlit subjects, and there are cameras compensating for light coming through the viewfinder, so I was trying not to let too much light in. Focal length - I'd say there may be a tiny difference in how bright image is formed with advanced viewfinders (fresnel lenses etc.), but it's only a speculation, and the difference can't be that big.
Initially I've noticed strange behavior of both bodies: one was acting strange in low light, while other was more lens-dependent. One gave greater variance, than the other. First issue is simple to explain - Carena doesn't work in low light, I have to live with it. Second issue was a bit harder, related to the measurement itself - Carena gives green light for way more, than 1/2 fstop range, while OK for me in Ricoh was within 1/3 fstop range. I'm quite happy to pin-point such issues and their outcomes... So I've reduced down amount of tested factors, getting rid of Carena body from the equation. I've eliminated battery issues with Ricoh and I've been left only with three lenses, rather than four, as the aperture tongue in my Revuenon, being off by 2.2mm, makes any testing with this lens pointless.
My only conclusion is 0.6mm of deviation within aperture transfer mechanism is enough to introduce considerable error. Smaller, than what Carena allows, but enough to confuse me with what Ricoh shows. so I'll have to trust my external light meter at least now and then, and I'll try to service Pentax-M lens myself, I hope it's doable with grinding stone in worst case, or screwdriver alone if things are designed to do it this way. For now, I'm unable to do anything more.