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

for _ in range(int(input())):
    n=int(input())
    l=list(map(int,input().split()))
    if(len(set(l))==1):
        print(-1)
        continue
    a=min(l)
    b=l.index(a)
    if(b==n-1):
        if(n>=3):
            if(l[-3]>l[-2]):
                print(b-1)
            else:
                print(b)
        else:
            print(b)
    elif(b==0):
        if(n>=3):
            if(l[2]>l[1]):
                print(3)
            else:
                print(2)
        else:
            print(2)
    else:
        if(l[b-1]>l[b+1]):
            print(b)
        elif(l[b-1]<l[b+1]):
            print(b+2)
        else:
            print(b+2)
