I've found myself editing the Points and Rewards plugin to make it work in the way my client has requested. I've added the following filters:

file: class-wc-points-rewards-discount.php line 81
code: $data = applyfilters('wcpointsrewardsdiscount_data', $data);
Reason: adjust coupon options as client didn't want loyalty points to be redeemed against sale items or used in conjunction with other discounts.

file: class-wc-points-rewards-manager.php line 562
code: $amount = applyfilters('wcpointsrewardsproduct_amount', $amount);
Reason: Client requested that amounts were rounded down before points are calculated. So a product costing £3.99 would earn the same points as a product costing £3.00 or £3.50. Whereas £4.00 would earn more.