The APRS-IS system really doesn't know if a packet arrived via HF or VHF. I suspect the reason you're getting VHF stations is that you have not changed the default Configure / General / Range of 50 miles to be something smaller, like 1 or 0. APRSISCE/32 automatically provides a filter for the APRS-IS and the Range is included in that filter resulting in "close" stations being received with no user effort (unlike some other clients that require entry of a filter to receive anything).
Also make sure that you don't have anything in Configure / General / Add Filter because that will also cause APRS-IS traffic to be received.
Another way is to check View / None followed by View / RF / All. This will cause the map to only show stations that you received on your own RF port and will suppress everything received from the APRS-IS.
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32