There are many reasons why a mock orange will have few blooms but lack of full sun is the most common. This shrub also likes moist soil so water when dry and add a mulch to seal in moisture.  If your shrubs are getting plenty of sunshine and water then some renewal pruning and fertilizer may give them the boost they need to fill in and flower more heavily. The first thing you need to understand is that pruning now or in early spring will remove all the flower buds for this coming summer. You may want to wait until the shrubs are done blooming in  late spring and then prune them back hard to encourage thicker growth. Aim to remove one third of the weakest or thinnest canes. Cut these all the way back so that there is just a few inches of stem poking up from the ground. Cutting back the branches will encourage fuller, thicker growth. Next you can add fertilizer. Do not use a high nitrogen plant food (keep lawn foods away)  but instead a complete fertilizer with micro and macro nutrients such as Osmocote will provide for any lack of nutrients that could be causing the poor flower production. Just apply the Osmocote around the base of the shrubs following the amount recommended on the label - from the photo I would guess about half a cup for each shrub. You only need to apply the Osmocote once in the spring. It will continue feeding all summer. One more tip. Many flowering shrubs do not produce a lot of blooms until they are fully mature and well established. This means seven to ten years in the ground. Your mock orange could be full of fragrant white blooms by next summer. Let us know how they do and Keep Growing, Marianne Binetti