As visible in the attached screenshot, this Tinkerer says their makeshift parts are "pretty effective for their mass", which implies that the parts are of lower mass but still as/more effective than same-mass non-makeshift parts.
However, one of the parts here is a Mak. Transmission Jammer, which has a higher mass than its same-range counterpart.
The only way it can be considered more effective is with its energy cost, but it still has a higher mass than any other Transmission Jammer.
It's probably normal in some way, but unless i'm being annoying by posting so many of these bug reports i'll keep posting what feels wrong to avoid not reporting an actual bug.