Length refers to the length of penetration, right? That's fine, but if it's as wide as a doorway, it's not so good! Because a long house (similar to a school classroom) does not gather energy.
It’s good if it goes deep, but of course the design must have reasonable ventilation and lighting! The courtyards of ancient mansions were very long and deep, but they would open patios to absorb light.
The most important thing in Feng Shui of a house is to have good Qi, good lighting, and no unfavorable mountain buildings around (this can only be known on site). If there is a dragon vein in the back, it will be a superior house.