If you can pop the sheathing off the bottom of the cantilever it's worth opening it up and air-sealing the framing to the subfloor, then stuffing full-depth high-density fiberglass or rock wool batts (R30) in there, or compress an unfaced R38 batt in there (easiser said than done, but probably cheaper.) Having the gap above the insulation is a "thermal bypass" path, for infiltration air to get in and chill the floor. The original insulation SHOULD have been snugged up the subfloor, not resting on the sheathing, since it's the cold sheathing that would potentially benefit from the ventilation gap for drying, not the sub-floor.
You don't absolutely need a vapor retarder for insulating the underside of a cantilever, but if you want to limit the mold/rot potential of the sheathing, staple 6-mil poly to the underside of the subfloor prior to air-sealing with foam, then seal the poly to the subfloor & joists with the foam.
If there isn't sufficient headroom room to re-build it from the bottom side, you can drill a 1.25" holes through the rim joist just below the rim joist and blow as much cellulose as you can stuff in there with a rental blower (you may have to use a reducing coupling taped to the end of the hose if the blower equipment doesn't come with a narrowing nozzle.) Cellulose is very air-retardent even at low density, and will reduce the air infiltration by 90% or more, while increasing the R-value to about R26-R27.
For the band joists in other areas you can cut'n'cobble 2" thick rigid EPS (~R8) cut with a 1/4-1/2" gap around the edges, lightly tacked in place, then fill the perimeter gaps with can-foam for a perfect air seal. Then put R15 rock wool trimmed for a friction fit to the interior side of that. With R8 foam & R15 rock wool you'll have minimal condensation at the foam/fiber boundary in your climate, and the vapor retardency of the foam will be sufficient to protect the band joist.
(^^Looks like they could have cut it a bit narrower before sealing to allow more fill with can-foam here- the air seal is less than perfect in places. The also used XPS, which could also be used, but it's more expensive, and lower vapor permenace, which limits the drying capacity toward the interior. In your climate EPS is a better choice, as long as it's at least R8, and not more than R12.)
If there is a ledge of concrete between the edge of the foundation sill in the interior, cutting in some 1.5" thick rigid foam and can-foam sealing it to the foundation sill AND concrete is advisable. Then stack a layer of rigid foam atop the foundation sill snugged up to the band-joist foam, and seal it in place, to protect the foundation sill from interior moisture drives in winter.
Alternatively, you could use 2" of closed cell spray polyurethane instead of cut'n'cobbled foam, which is likely to air seal better. You'll still want R15 rock wool on the interior side to fatten out the R-value, and as a thermal break against fire lighting off the foam.
If it's a full basement (or even a crawlspace) it's worth insulating the foundation walls too, but I won't detail that here unless asked.