An important question might be; how old are you? The metabolism will slow as we age, producing extra body fat, that thickness that was referred to. . First signs are usually around the lower belly and hip area. Cardio is good, but what kind of cardio may make a difference. Running 30-45 minutes , every day, is no insurance that body fat will be lost. Check out some marathon, and half marathon, runners and you may notice thick skin and weight around the ab's. Skinny fat is not foreign to some of them. Tri athletes seem in better shape.
Might consider doing a search on interval training, where short burst of effort followed by brief rest periods, may draw your interest. You do not have to be stuck with running only for superior cario endurance and fat loss. Interval training can gear up the metabolism very well and can be used twice to three times weekly. Can work in well with any BB'ing scheme.
Perhaps a little adjustment in a lower carb range could help also. Try hitting 100 to 150 grams of carbs daily and see what happens. Some athletes hold to 40-60 grams a day, for a short period, while keeping the good quality cal's up to the 3000 (or more) daily. Can break the pattern of lower carbs a bit on the weekends with pizza, in-n-outs, fruits/vegies, etc. Good Luck
Side Bar: I, myself, would never suggest having a arm's only work out day. More of a lat/bicep or chest/triceps thing. But if it works for you, than great.