1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

def all_same(a):
    x=a[0]
    n=len(a)
    for i in range(n):
        if(a[i]!=x):
            return False
    return True
t=int(input())

while t>0:
    t-=1
    n=int(input())
    a=list(map(int,input().strip().split()))
    x=a[0]
    d=False
    if(all_same(a)):
        print(-1)
    else:
        x=max(a)
        for i in range(n):
            if i==0 and a[i]==x and a[i+1]<x:
                print(1)
                break
            elif i==n-1 and a[i]==x and a[i-1]<x:
                print(n)
                break
            elif i<n-1 and i>0:
                if  a[i]==x and ( a[i-1]<x or  a[i+1]<x):
                    print(i+1)
                    break
'''
6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
'''