If solid rubber pucks or blocks were arranged so that they'd have to compress to absorb the large motions that occur in a 200kg (450 lb) engine, a huge amount of it would be transmitted through to the chassis side. By arranging them at an angle, a lot of twisting motion can be absorbed as the mounting plates (of each mount) slide back and forth, and vertical motions during bumps and secondary resonance* are split between all three mounts (the rear one is angled too).

You have to look at the history of the 700 series to understand why the liquid mount was used. It was introduced as the 760 V-6 luxury car. The lower line 740 came a year later. A lot of NVH (noise, vibration, harshness) refinements were added to allow the luxury 700 line to compete in the US market, especially when the choice was made to add the 4 cylinder turbo option to the 760 model around '88 or '89. Automatic transmissions are "loaded" at idle through the fluid coupling known as the torque converter. Any unevenness in the cylinder firing will change the total load and transmit a "shake" to the chassis. Manual transmissions are either declutched or left in neutral while idling. What's the first thing people do to eliminate a rough idle in an auto gearbox car? Pop it out of drive at lights.

*Secondary vibration is a natural occurrence on inline engine whose firing space is divisible only by 180° or multiples of it. In short, all straight 2 and 4 cylinder engines. This eliminates 3, 5, 6, 8 and 12 cylinder inlines, all vee and opposed type engines as generators of it. It is caused by a combination of the momentary radial (rotational) acceleration of the crankshaft during a power stroke and the lateral (vertical) acceleration of the block caused by the inertia of the piston/connection rod changing direction at top and bottom dead centres. The only possible spacing of these pulses on an I-4 is end cyl - next to end - end cyl - next to end, as in #1, #3, #4, #2 or 1-2-4-3. This causes a figure-8 wobble at twice the speed of the engine that causes a high speed buzz that four cylinder engines are known for. Counteracting this secondary vibration is EXACTLY what the balance shaft found in 16 valve B234F and white engines was put there for.

Back to the fluid mounts; the viscosity of the silicone gel was selected to prevent those vibrations from traveling all the way through the mount and into the chassis, more effectively than the rubber ones could.