Coupld of Questions :
1. who is the IP provider, is this your IP address space ?
2. If the IP given by ISP 1, so the route always takes ISP 1 routing to your network.
3. what you can do is Regsiter the Domain with ISP2 IP address also, do the Round Robin DNS or need to get reverse proxy from Cloud provider to make it happen.
IP SLA works internal to external failover based on the tracking.
If you Like external to internal you need to feddle with DNS Entries with TTL - kind of Auto script - but there is small downtime,
If you do not like this down time reverse proxy with Dual ISP address, so it automatically NAT to your Local IP address ?
is this make sense ?