The SSR4 is limited to 1 amp per channel without a heatsink and 2 amps with it for good reasons. This is not a triac issue but heat dissipation/traces/connector rating/safety issue.
This is a quote from RJ. Tried to copy the link from the post but phone not cooperating. If you'd like to view it , search on SSR4 load. In the results see the thread on Lynx SSR4: Higher amps.
Leon