Extra small agaves (again courtesy of Greg Starr's book):
albopilosa (8-16") ($$$)
isthmensis (6-15") (usually clumping)
macroacantha (10-18") (also a clumper)
parviflora (6-12") (solitary or offsetting)
polianthiflora (8-15") (nice flowers)
toumeyana bella (6-8") (extra small variety of this species)
utahensis (10-16") (dry growing plant in nature, not good for your climate)
Some of those would work great in a container long term, others would require periodic attention to remove offsets. There are also variegated forms of various plants which are smaller than the normal version of the species.
Worth looking at, given you receive 43" of annual rainfall, is Starr's list of 10 most mesic species (ie. plants which will better tolerate wet conditions): bovicornuta, geminiflora, gentryi, horrida, isthmensis, mitis, montana, petrophila, schidigera, wocomahi. Perhaps you will get the best results at the intersection of those two lists, and generally try to avoid the small(ish) plants on his list of the 10 most xeric (dry-growing) species, namely toumeyana, utahensis, vic-reginae. Or just be sure to give them extra sharp drainage.
The small(ish) agaves that I have kept in containers which could be overwintered: victoriae-reginae compacta (the smaller, offsetting form) (to 10"+ if kept solitary); univittata "Quadricolor" (needs annual depupping if kept in a 10" pot); utahensis; isthmensis (needs to be split every few years); geminiflora (for a few years anyway); macroacantha (for a while anyway); "Bloodspot" (other Mangaves make excellent container plants); "Kichiokan" (and its relative "Kichijokan" for a while anyway); nizandensis; oteroi; shawii dwarf; A. maculata (ex-Manfreda maculosa) (for now anyway); A. undulata.
Some pics to illustrate a few favorites from this general category, in no particular order:
Stush would probably be able to give you the best suggestions for plants that work with overwintering.
Also see this old thread from 5 years ago:
The thread "Agaves that don't get huge" in
Cactus and Succulents forum
