The Ford Focus has been on a torrid sales pace, with deliveries up 43.8% through May to 110,237 units, according to WardsAuto data.

But while Focus has been flying off dealer lots, the same cannot be said for its smaller sibling, the Fiesta, with 2012 sales down 27.0% vs. year-ago to date.

That disparity is no surprise, Ford U.S. sales analyst Erich Merkle says, noting the percentage split between subcompact and compact cars industrywide normally runs 25/75, and sometimes 20/80.

Last month, Focus sales totaled 24,769, up 2.5% on a daily basis (two more selling days this year than in like-2011), while Fiesta deliveries dipped 21.2% to 6,080.

The mix was 94% Focus when the Fiesta began selling in volume in June 2010, but the smaller car gradually increased its share, peaking at 37% in February 2011, according to WardsAuto data. In May, the Fiesta/Focus split was 20/80.

Merkle says Fiesta’s stronger showing last year was a result of low Focus stocks last spring.

“For five months (Focus inventory) was below 20,000 units,” he says. “It should be in the high 30,000s or even 40,000. Because there was limited inventory (of Focus) when gas prices went up, the Fiesta benefited by default.”

Sales elsewhere reflect similar splits to what the Fiesta and Focus show today.

The sales ratio of the Chevrolet Sonic subcompact and Cruze compact was 27/73 in May, while the split between the Toyota Yaris and bigger Corolla was 10/90.

Other than the Fiesta, most other Ford vehicles posted positive results last month. Overall Ford sales were up 3.9% to 212,859.

Light-truck deliveries were particularly healthy, rising 7.9% vs. year-ago to 132,971. Strong performers included the F-Series, with sales climbing 20.3%, and the Transit Connect, which turned in its best monthly performance ever, with 3,937 sold, a 40.8% increase.

Escape cross/utility vehicle demand was off 12.9% to 20,769 units. Ford last month began delivery of the new ’13 Escape and is in the process of selling down remaining ’12 models.

Sales of Ford Edge and Explorer CUVs rose 14.3% and 7.7%, respectively.

Car sales were off 2.1% to 79,888, but several key models posted stellar months. Mustang deliveries in May soared 45.7% to 10,427, outselling key rival Chevrolet Camaro by 1,404 units.

Ken Czubay, Ford vice president-U.S. marketing, says some Mustang sales were to fleets, but the majority was to retail customers.

The Ford Fusion midsize sedan notched its best May sales ever and its strongest-ever retail volume month, with deliveries up 0.6% to 25,514 vehicles.

Like the Escape, Ford is selling down current-generation Fusions to make way for the all-new ’13 model arriving this fall.

Ford ended the month with 448,000 vehicles in stock, including 137,000 cars, 188,000 trucks and 123,000 utility vehicles.