It’s called “self sealing” shingles (or lack thereof).
Shingles are made to self seal to each other by having the sun heat them up (including the asphalt strip on the underside) and the weight of the shingle will cause the asphalt to press into the lower shingle.
When the shingle is hung at more than about 6:12 or in a cool environment, then the weight does not affect the shingle and it does not stick to the lower shingle.
Often “hand tabbing” is required. Hand tabbing is merely “hand applying” a glob of asphalt about the size of a quarter to the lower shingle about every 12” on center and then stepping on the upper shingle to squish it flat.
Without the shingles sticking together, they are susceptible to “blow off” in high wind areas.
In your case, use a single glob for the small shingle. Do not coat the entire area, because the shingle will heat up from the sun and need to move and expand.