If you don't have a polyester ball for corner spares, I would suggest picking one up from your Pro Shop
. Especially if you play on drier lane conditions, your strike ball will be more difficult to control when you are touching so much of the lane. Remember that different parts of the lane have different amounts of oil. One way to take the lane out of the equation as much as possible is to throw a polyester ball at your corner pins. As a matter of fact, I always use my old polyester ball for the 4,6,7 and 10 pin spares.
There is no need to use your strike ball on a single pin spare since carry is not an issue. All you have to do is make contact with the pin for it to go down. Remember that on single pin spares, you have a huge 13 inches of area to knock that pin down. This 13 inch margin of error is calculated from the width of the pin plus twice the width of the bowling ball.
I'll also give you a quick reasoning by going cross-lane at corner pins. We shoot cross-lane at corner pins to increase our margin of error. Since the corner pins are on the edge of the lane, we lose some mistake area on the side of the channel. By increasing our angle on corner pins, we are effectively making more mistake area on the side of the channel. Bowling is a game of percentages. Increasing your angle on corner pin spares increases your percentage of picking them up by giving you more mistake area.